1. Field of the Invention
The present invention relates to bis(silyl)methanes and a process for preparing the same by directly reacting .alpha.-chloromethylsilanes represented by the general formula I incorporated with hydrogen chloride or alkylchlorides represented by the general formula II, with silicon metal to give the bis(silyl)methane compound having dichlorosily group (formula III) as the major products and the bis(silyl)methane compounds having trichlorosilyl group(formula IV) in moderately high yields in the presence of copper catalyst at a temperature from 250.degree. C. to 350.degree. C. The preferred reaction temperature range is 300.degree.-330.degree. C. Useful copper catalysts include copper metal, copper salts, and partially oxidized copper. ##STR2##
In formula I, R.sub.1, R.sub.2, and R.sub.3 are independently methyl group or chlorine atom. EQU RCl (II)
In formula II, R is hydrogen, alkyl (C.sub.1 -C.sub.4), CH.sub.2 CH.sub.2 Cl. ##STR3##
In formula III, R.sub.1, R.sub.2, and R.sub.3 are independently methyl group or chlorine atom. ##STR4##
In formula IV, R.sub.1, R.sub.2, and R.sub.3 are independently methyl group or chlorine atom.
2. Description of the Prior Art
Trichlorosilane is a very important starting material for semiconductor grade silicon and also for silicones, because it undergoes hydrosilylation reaction to the unsaturated organic compounds. Trichlorosilane is commercially manufactured by the direct reaction of elemental silicon with hydrogen chloride in the presence of copper catalyst (A. D. Petrov, B. E. Mironov, V. A. Ponomaren Ko, and E. A. Chernyshev, "Synthesis of Organosilicon Monomers" Consultants Bureau, New York, 1964). The reaction is carried out at 200.degree.-500.degree. C. and gives trichlorisalane as the major product and tetrachlorosilane, hydrogen, and dichlorosilane as the minor products. The reaction conditions such as the nature of the starting materials, the catalyst, the reaction temperature, the reaction pressure, the type of reactor used etc. should be optimized to get the maximum yield of trichlorosilane. EQU Si+HCl.fwdarw.HSiCl.sub.3 +SiCl.sub.4 +H.sub.2
Methyldichlorosilane which has methyl group and hydrogen on silicon is frequently used in the manufacture of modified silicone fluids and room temperature vulcanizing silicone rubbers. Methyldichlorosilane is obtained in about 3% yield as a by-product from the direct reaction of elemental silicon with methyl chloride (R. J. H. Voorhoeve, Organohalosilanes: Precursors to silicones, Elsevier Publishing Company, New York, 1967). EQU Si+CH.sub.3 Cl.fwdarw.(CH.sub.3).sub.2 SiCl.sub.2 +CH.sub.3 HSiCl.sub.2 (-3%)
Yamada reported that methyldichlorosilane could be prepared in higher yields by reacting elemental silicon with the mixed gases of methyl chloride and hydrogen chloride (S. Yamada and E. Yasunaga, Japanese Patent 6162(1952). Halm also reported that methyldichlorosilane could be obtained up to 9.5% yield by adding 15% of hydrogen chloride to methyl chloride in the direct synthesis of methylchlorosilanes (R. L. Halm and R. H. Zapp, U.S. Pat. No. 4,966,986).
In 1953, Petrov and his co-workers reported that the yield of alkyldichlorosilane increased in the direct reaction of elemental silicon with alkyl chloride as the bulkiness of the alkyl group increased. They obtained 30% yield of butyldichlorosilane from the reaction of elemental silicon with butyl chloride (A. D. Petrov, N. P. Smetankina and G. I. Nikishin, Zh. Obshch, Khim, 25, 2332 (1953), CA 50-9280). This was explained by that butyl chloride decomposed to give off hydrogen chloride and the mixed gases of butyl chloride and hydrogen chloride reacted with elemental silicon to give butyldichlorosilane. EQU Si+BuCl.fwdarw.BuHSiCl.sub.2
Fritz and his co-worker first reported that Si-H containing bis (trichlorosilyl) (dichlorosilyl)methane was obtained in about 3% as a byproduct from the direct reaction of elemental silicon with methylene chloride in the presence of copper catalyst at 280.degree. C. (G. Fritz and H. Thielking, Z. Anorg. u. Allgem. Chem., 306,39 (1960). In this case, the yield was not very high and the decomposition of methylene chloride easily deactivated the elemental silicon and copper catalyst and made the process economically less feasible.
In 1957, Dannels and Post reported that bis(trimethylsilyl) (dichlorosilyl)methane was prepared by reacting trimethylsilylmethylmagnesium bromide with trichlorosilane in 64% yield (B. F. Dannels and H. W. Post, J. Org. Chem., 22, 748 (1957). However, the Grignard reagent costs high and the process requires handling of highly flammable ether solvent. This make the process economically less feasible.
In 1974, Sommer and his co-workers reported that bis (dimethylchlorosilyl) (dichlorosilyl)methane was obtained in 22% yield from the co-pyrolysis of dimethylsilacyclobutane with trichlorosilane at 611.degree. C. The starting cyclic compound was again prepared by Grignard method.
We also reported that the trisilaalkanes represented by the general formula V as the major products and bissilylmethanes represented by the general formula IV as the minor products were prepared by reacting .alpha.-chloromethylsilanes represented by the general formula I with elemental silicon in the presence of copper catalyst at a temperature from 250.degree.-350.degree. C. The copper catalyst was used 1-20% of total contact mixture, but the preferred amount was 5-10%. The reaction could be carried out in a fluidized bed or in a stirred bed reactor. Addition of microspherical acid clay to silicon metal improved the fluidization and gave better results (I.N. Jung, G. H. Lee, S. H. Yeon, M. Suk, U.S. patent application, Ser. No. 07/697,165 (May 8, 1991). ##STR5## wherein R.sub.1, R.sub.2, and R.sub.3 represent independently chlorine atom or methyl group.